Leading influenza researchers published a letter in the Jan. 24 and 25, 2013, issues of Nature and Science, respectively, declaring an end to a voluntary moratorium on research about how the H5N1 avian influenza could become easily transmissible from person to person, though with a notable exception: "Scientists should not restart their work in countries where, as yet, no decision has been reached on the conditions for H5N1 virus transmission research," they wrote in their letter.